1. Field of the Invention
The present invention relates to a process for, and to the use of specific spray technology for, impregnating porous mineral substrates to provide water-repellency and, where appropriate, oil-repellency and, where appropriate, also dirt repellency and graffiti repellency, in particular for treating construction materials.
2. Discussion of the Background
It has long been known that porous mineral substrates, i.e. construction materials, such as fiber-filled concrete, concrete, sandstone, limestone, natural stone, artificial stone, glass wool items, mineral wool items, bricks, artificial stone, mortar, render, terracotta, ceramics, calcium silicate brick, fiber-filled concrete panels, and also mineral-fiber-filled panels, and cement- or clay-bound construction materials can be protected by applying hydrophobicizing impregnating agents to provide effective resistance to moisture penetration. There are a large number of liquid impregnating agents suitable for this purpose. There are commercially available products based on natural and synthetic waxes and oils; on metal soaps, such as stearates; on synthetic resins, such as acrylate resins, epoxy resins, alkyd resins, or polyurethane resins; or on silicon-based products, such as alkylalkoxysilanes, alkylalkoxysiloxanes, silicones, and also silicone resins. It is also possible to achieve oleophobic properties by using fluorinated products, e.g. Teflon, modified fluoroalkyl resins, fluoroalkylalkoxysilanes, fluoroalkylalkoxysiloxanes, fluoroalkylhydroxysiloxanes, or fluorosilicones.
The advantages of these processes for providing hydrophobic or oleophobic properties are described in the literature and are well known to the skilled worker. The methods for describing the effectiveness of processes for providing hydrophobic or oleophobic properties are likewise known from the literature. Examples which may be mentioned here are, for hydrophobicization, the penetration depth and the reduction in water absorption; and for oleophobic properties and antigraffiti properties the functional test described in the set of regulations for “Bewertung von Verfahren, Technologien and Materialien zur Graffitientfemung und Graffitiprophylaxe” (Assessment of processes, technologies, and materials for graffiti removal and graffiti prevention) (ReGG) issued by the Gutegemeinschaft Antigraffiti, Copyright 2000 by Labor Dr. Kupfer, Alt Stralau 54, 10245 Berlin.
Liquid impregnating agents are generally applied to saturation by flow-coating processes, such as spreading, spraying, dipping, for example using a brush or roller, or using a Birchmeier spray, or using airless devices (Series of publications by MBT AG, Meynadier “Bautenschutz and Instandsetzung, Teil 1: Partielle Instandsetzung und Oberflachenschutz (Protection and repair of buildings, part 1: partial repair and surface protection), No. 4 January 2000, ISBN 3-907075-04-8, pp. 92, 95, and 98; “Verarbeitungshinweise fur DYNASYLAN® BHN and BSM 40%” (Usage instructions for DYNASYLANV BHN and BSM 40%), October 1995, Hüls A G; “WackerSilicone fur den Denkmalschutz” (Wacker silicones for protection of historic buildings), April 1975, p. 6; Dr. M. Roth in Bautenschutzmittel Sonderdruck “Anstriche und Impragnierungen auf Naturstein” (Paints and impregnating materials on natural stone), Wacker Chemie GmbH; “Wackersilicone Bautenschutzmittel” (Wacker silicones for protection of buildings), May 1981, p. 35 10; product information relating to Wacker BS® SMK 1311, Wacker BS® 1001, Wacker BS® 1701, Wacker BS® 290, Wacker BS® Creme C, Wacker BS® 28, Wacker BS® 29 (all dated March 2001)).
A disadvantage of these flow-coating processes is that the amount of liquid impregnating agent applied is always the amount which the construction material is capable of absorbing (cf., for example, series of publications by MBT, Meynadier Bautenschutz mit Hydrophobieren (Protection of buildings, using hydrophobicizing processes), No. 2, March 1999, R. Hager “Silicones for hydrophobicization”, p. 16). In the case of highly absorbent substrates, therefore, additional dilution of the impregnating agent is necessary, in order to avoid excessive consumption of product and moreover to avoid severe local variations in the result of hydrophobicization.
For example, if an absorbent brick is treated by the flow-coating process, the consumption of product can be about 1 l/m2 or more. If a concentrated, i.e. solvent-free, product is used in this way the result is unnecessarily high consumption of product, resulting in high costs and often also a performance disadvantage. For example, in instances where use is made of siloxane- and silicone-resin-based products, a tacky resin film which is esthetically unattractive is produced on the surface. In the case of substances with good penetration, for example monomeric alkyl-trialkoxysilanes or short-chain alkylalkoxy-siloxanes, a penetration depth of the order of centimeters results when such high amounts are applied to absorbent substrates. Since these active ingredients are expensive and a penetration depth in the region of about 1 cm is generally sufficient for the desired action, solvents are used to dilute the valuable active ingredients. In the case of emulsion systems water may be used, and in the case of solvent-based systems alcohols or petroleum hydrocarbons may be used. However, a disadvantage is that solvents pass into the atmosphere and, respectively, that some construction materials exhibit long drying times when water-based products are used, and this is particularly disadvantageous when fiber-filled concrete panels, for example, are hydrophobicized at the factory, since the production process includes an additional drying step.
In addition, multiple wet-on-wet application is usually recommended for liquid impregnating agents in order to achieve maximum uniformity of product application. For example, the Hüls brochure relating to the protection of buildings recommends under “Verarbeitungshinweise for DYNASYLAN® BHN and BSM 40%” (Usage instructions for DYNASYLAN® BHN and BSM 40%) that there should be a visible reflective liquid run-off curtain of length from 30 to 50 cm on vertical surfaces. Another way of achieving this effect on relatively small areas is to pour the material from a can onto the vertical surface. High-pressure misting of the impregnating liquid, for example as achieved by the airless technique, and also during Birchmeier spraying, should be avoided since firstly the aerosol droplets formed are hazardous to health and secondly considerable product losses can occur through evaporation and overspray. The airless technique generally uses nozzle internal pressures >2 bar. For example, in the painting industry the pressure range from 7 to 14 bar is usually used for the airless technique, producing very fine spray mists.
Absorbent substrates, such as some natural stones, e.g. Euville or Savonnieres, and also fiber-filled concrete components or mineral-fiber insulating boards, have such high porosity that the resultant material consumption here is of the order of kilograms per square meter, in particular if the recommended double flow-coating process is used. In order to control the active ingredient content in such cases, dilute solutions or dilute emulsions are used. This has the disadvantage that either it is necessary to use solvents or the active ingredients have to be processed by a complicated method to give water-dilutable emulsions.
When prefabricated components are impregnated in the factory, the use of solvents is particularly disadvantageous, since in the case of organic solvents the evaporation process can produce explosive mixtures with air, and when water is used as solvent (emulsions) long drying times have to be accepted. In addition, there are environmental disadvantages with the use of solvents in the hydrophobicization of, for example, existing facades.
The flow-coating process to saturation is also used in antigraffiti impregnation. An improved multistage process for antigraffiti impregnation is disclosed in EP 1 193 302. Here, the first application of the antigraffiti impregnating agent takes place from dilute solution in order to control consumption of product. Further applications take place using a device equivalent to a Birchmeier spray (Gloria sprayer, operating pressure 3 bar). A disadvantage here is that the first application of product takes place from dilute solution, causing increased manpower cost and relatively high drying times, and that from the second application pass the spray mists produced can pose problems, together with the need, apparently resulting from slightly non-uniform application of material, to carry out mechanical finishing. The result of this can be higher consumption of material and longer waiting times between application of the individual layers.
Use of the air-supported HVLP (high volume low pressure) and LVLP (low volume low pressure) spraying techniques for painting is known.